In general, ink jet printing machines or printers include at least one printhead unit that ejects drops or jets of liquid ink onto an image receiving surface such as an image substrate. A phase change ink jet printer employs phase change inks that are in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. The melted ink can then be ejected as drops or jets by a printhead assembly onto an image substrate at the elevated operating temperature of the machine or printer. The image receiving surface may be a recording media in which case the ink can be ejected directly onto the image substrate, or, alternatively, an intermediate transfer surface in which case the ink is ejected onto the intermediate transfer surface and subsequently transferred to a recording media.
A color printer typically uses four colors of ink (yellow, cyan, magenta, and black). In a phase change ink, or solid ink printer, ink sticks of each of these colors are typically inserted into an ink loading station and subsequently delivered to a melting station which heats the solid ink sticks to a melting temperature and supplies the melted ink to the printhead assembly. In order to print multicolor images, ink jet printers, including solid ink printers, have used a halftone imaging process. As is known in the art, in halftone imaging, an input image may be divided into a series of color separated images, each one of which corresponds to a primary color in the input image. Each color separated image is printed with a complementary ink marking material in a primary color or a colorant which is the subtractive complement of the color separated image. Superimposing the printed color separated images, in registration, on one another produces a pattern of different primary colors or their subtractive compliments that the human eye perceives as a composite color image rather than the color separated images.
The range of colors that can be produced by halftone processes is determined by the number of primary colors that are used and the colors of those primaries. Generally a four-color process is employed using cyan, magenta, yellow and black primary colors. In order to expand the range of colors that may be produced by halftone processes, the printer may be augmented with additional ink colors beyond the usual four primary colors. For example, in a solid ink printer, solid ink sticks having colors other than cyan, magenta, yellow and black may be used such as orange, green, etc. These additional inks may be used to extend the color gamut of the halftone process color output.
Customer selectable colors are typically utilized to provide instant identification and authenticity to a document. As such, the customer is usually highly concerned that the color meets particular color specifications. A more specialized example of customer selectable color output can be found in the field of “custom color”, which specifically refers to registered proprietary colors, such as those used, for example, in corporate logos, authorized letterhead and official seals. Because of the importance of customer-selected color to high-end printing, most printers that support color printing allow specification of colors by indicating a name or number defined in a specification system such as the Pantone Matching System or Pantone Goe System, or by coordinates in some color description coordination and/or space, such as CIELAB's L*a*b* coordinates.
There are many colors available using the Pantone system or other color formula guides of this nature, however, that may not be adequately produced via typical half tone process color methods. For example, custom colors may be difficult to accurately generate via halftone methods because the production of solid image areas of a particular color using halftone techniques typically yields non-uniformity of the color in the image area, which can be objectionable in some applications. Moreover, lines and text produced by halftone methods are very sensitive to misregistration of the multiple color images such that blurring, color variances, and other image quality defects may result.
In previously known solid ink printing systems, custom color printing has been carried out by providing solid ink sticks comprised of a premixed phase change ink composition made up of a mixture of multiple color inks blended in preselected concentrations for producing the desired custom color output. Custom color ink sticks are typically prepared at an off-site facility for subsequent delivery to the customer. For example, a customer can order a desired color of ink stick from an ink supplier. This process is commonly facilitated by reference to a name or number defined in a color specification system, e.g., Pantone number. Pantone colors typically have a “recipe” associated with them that defines, for example, a ratio of basic color components that are used to produce the desired color. The ink supplier mixes the component inks according to the Pantone recipe to produce the desired color and delivers the premixed custom color ink sticks to the customer. Because customer selectable colors are typically manufactured at an off-site location, however, supplies of each customer selectable color ink stick may have to be ordered well in advance of their actual use. In addition, customers may be required to order large quantities of the custom color ink sticks from the ink supplier, which may be more than they require or cost more money than they desire to spend.